The present invention relates to micromechanical resonators. In particular, the present invention is related to a new class of contour-mode piezoelectric micromechanical resonators that can be employed as building blocks in wireless communication components such as filters and oscillators.
Recent demand in wireless communication for miniaturized, low-power, low-cost, on-chip and high-Q resonators to be employed in front-end RF filters or as frequency references has focused research efforts towards the development of new vibrating micromechanical structures, capable of substituting existing off-chip, bulky resonator technologies. Some promising alternatives to currently adopted solutions (SAW or ceramic devices) have been demonstrated (e.g., see, Li et al., IEEE MEMS, 821-824 (2004); and Wang et al, IEEE MEMS, 641-644 (2004)) using in-plane, electrostatically-transduced, micromechanical resonators made of polysilicon or polydiamond. Although high quality factors have been reported at ultra high frequency range (UHF), the exhibited impedance values are too high for these resonators to be directly coupled to antennas in RF systems. Also, the high temperature fabrication steps involved with the deposition of the structural layers ultimately complicate the integration of these devices with state-of-the-art microelectronic components.
Film Bulk Acoustic Resonator (FBAR) technology (e.g., see, Aigner et al., Transducers, 891-894 (2003); and Ruby et al., IEEE International Solid-State Circuits Conference, 121-122) has proven itself as a valid solution to replace conventional RF filters, demonstrating relatively high quality factors (Q˜2,500), and small (several Ω) impedances. The fundamental frequency of these devices is set by the film thickness. This constitutes a major challenge to the manufacturing of FBARs. On one hand, in order to obtain reasonable yields, a thickness tolerance of 0.1% is needed. On the other hand, multiple frequency selective arrays of resonators cannot readily be fabricated on a single chip, due to fact that the frequency of vibration for the devices is set by the film thickness.
There is therefore a need for an improved resonator that does not suffer from the design disadvantages of currently available resonators.